Safety Center Tower Grounding
Professionally Installed and Maintained Lightning Protection and Grounding Systems Ensure
Uptime and Reduce County’s Costly Repairs
Municipal safety centers typically
combine police, fire, 9-1-1 and other
emergency services – they must
remain operational at all times.
If communications systems fail,
dispatchers are helpless, emergency
workers can’t find each other and the
public could be at risk.
Victoria Wolber is the director
of emergency management and
communications for Macomb Country,
Michigan. She is based at COMTEC,
the county’s impressively rebuilt,
25,000 square feet safety center in Mt.
Clemens, Michigan in the southeastern
part of the state, (Cover).
“It’s critical that our communications
services remain up and running because
we’re often dealing with life-and-death
situations in our 9-1-1 dispatch center,
and we have to get our personnel to the
injured as fast as possible,” said Wolber.
All communications systems need
antenna towers, which naturally invite
lightning strikes that can cause damage
to a center’s sensitive equipment.
The solution: equip the towers with
robust, correctly designed and properly
installed lightning protection and
grounding systems to direct lightning
energy away from sensitive equipment
and harmlessly into the earth before it
damages equipment.
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The Macomb County, Michigan COMTEC safety
center was rebuilt from an existing structure
and upgraded to modern codes, including those
dealing with grounding and lightning protection.
It has never suffered lightning-induced damage.
“We knew that we had to call in experts who
understood the lightning protection and grounding
fields, knew our systems and knew what to do to
protect our critical assets,” said Wolber. “We did
that, and we’ve never had any lightning-caused
downtime here at COMTEC.”
Wolber and her electrical contractor hired Greg
Fair, a project manager and field superintendent
with Guardian Equipment Company, a Michiganbased firm that specializes in lightning protection.
Since COMTEC was relocating to an existing
structure with a pre-existing tower, the challenge
was to formulate a system that met the applicable
codes and accommodate the site’s components.
FIGURE 1.
The COMTEC center’s transmission tower was grounded when built, but age and corrosion had
deteriorated the connections. Upgrades during restoration of the center included exothermically
welded connections, new grounding electrodes and a buried copper ring ground.
During re-construction, the building’s open walls
helped Guardian Equipment advised the engineers
on designing and concealing the new grounding
system. The building’s antenna tower (Figure 1)
had previously been grounded, but the existing
mechanical connection method was found to be
inadequate. Existing connections to the tower
showed signs of aging. They were mechanical, in
one case using a simple water pipe connector, and
they had become loose over time. There was also
some corrosion, which increases ground resistance
(Figure 2).
FIGURE 2.
Tower-grounding cables were originally bonded with mechanical clamps such as the one shown at the far left foreground, but age and corrosion had loosened the
connections, raising ground resistance. The facility upgrade included replacing those connections with exothermically welded bonds and 28R Class II lightning
conductor cable, center.
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To aid in the new grounding system design, Fair
and his team referenced several codes that dealt
specifically with grounding for lightning protection:
Underwriters Laboratories’ UL96A: Installation
Requirements for Lightning Protection Systems,”
the National Fire Protection Association’s NFPA
780: Standard for the Installation of Lightning
Protection Systems, NFPA 780 and the Lightning
Protection Institute’s LPI 175: Standard for the
Design – Installation – Inspection of Lightning
Protection Systems. The well-known and often used
Motorola 56A, which also deals with towers, did not
fall within the scope of work.
Fair and his team began with a site survey to guide
their engineers in designing the work. Following
the survey, the team installed air terminals (also
called lightning rods, Franklin rods and strike
termination devices, STDs) at 20 foot intervals along
the roof’s perimeter and elsewhere on the roof. The
perimeter cable was used as a ring ground from
which to drop down-conductors to driven 10 feet x
¾-inch copper-clad electrodes in the ground below.
Approximately 15 driven electrodes were spaced
about 100 feet apart surrounding the structure.
Two of them specifically bonded to the ring-ground
surrounding the tower.
FIGURE 3.
Copper lightning cable is unobtrusive when mounted against brown or red-brown surfaces
such COMTEC’s brick walls. This property of the red metal is architecturally advantageous
when installing rooftop lightning protection systems.
“We grounded the tower with 28R cable, which is
a special Class II lightning conductor consisting of
28 strands of bare, braided AWG 14-Gage wire,”
said Fair. “We sometimes use tinned wire when our
engineer of record thinks that it would give the
conductor a longer service life, but that wasn’t the
case here.”
Class II cable is used for structures taller than 75
feet. It is also good when conductors have to be
exothermically welded to ground rods, building
steel, or in this case, to the tower itself.
“On the two-story side of the structure, which is
less than 75 feet tall, we used 29-strand x 17-Gage
Class I wire. It’s a little thinner and less obtrusive to
the eye,” said Fair (Figure 3).
FIGURE 4A.
A proper grounding cable connection to a gas service line. The silvery, copper-alloy,
UL-approved cable clamp is cadmium plated to prolong corrosion resistance.
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All services, such as electric, water and gas were
bonded together at a common ground potential
and bonded to the building’s grounding system,
in accordance with code requirements (Figures
4a and 4b). Fair tags his installations where
appropriate to inform workers of the Codesensitivity of those connections.
FIGURE 4B.
Grounding of the center’s water and gas service entrances is provided by the heavy-gage copper cable, right. The tag shown on the left alerts technicians that grounding
to gas and other services is code-mandated.
“We also bonded to exposed building steel,” said Fair.
“There are people who believe that using building steel
is not advisable because it can lead to side flashes
since the entire structure becomes energized when
a strike hits. But it won’t do that if the building is
properly grounded and if the sizes of the conductors
are adequate to provide the path the lightning current
preferentially follows, i.e. through the path of lowest
resistance and/or impedance (emphasis by Fair). We
provide that path.”
FIGURE 5.
When lightning strikes one of the nine auxiliary sites that the county operates, energy is
bled off the coax on the vertical run (Fig. 7), the coax where it penetrates the firewall (see
above), and the interior side of the firewall (Fig 9).
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Bonding the grounding system to building steel is also
a code-mandatory practice. However, while building
steel might provide a de facto ground/earth connection,
a continuous electrical path cannot always be verified
and grounding connections should properly be made
via adequately sized copper down-conductors bonded
to appropriately spaced, driven electrodes. A rooftoplevel ring-ground surrounding the structure might also
be employed, as was done at the COMTEC facility. The
ring simplified installation of the lightning protection/
grounding system, and its copper down-conductors,
blended in well with the center’s brick walls.
FIGURE 6.
One of several auxiliary transmission towers operated by Macomb County.
The towers extend emergency communications well beyond the range of
the COMTEC headquarters tower. All towers are equipped with the same
high-quality, all-copper grounding systems as those installed at COMTEC.
FIGURE 7.
A copper grounding bar is mounted on the tower approximately 10 feet above grade. The
six small-diameter cables leading upward from the bar connect to shields on cables and/or
waveguides leading down from antennas above. The two heavy grounding cables leading
downward from the bar are the down-conductors shown in Figure 9.
Auxiliary Transmission Facilities Equally Well Protected
Macomb County operates several auxiliary transmission
facilities that are located such that they provide emergency
communications to the county’s 850,000 residents throughout
the large 479 square miles jurisdiction. The auxiliary facilities
are each equipped with a tower (Figure 6). The towers, as well
as the facilities themselves, are protected from lightning strikes
by robust, all-copper grounding systems.
• Grounding connections from antennas, cables and shielded wave
guides on the tower are made to a ¼-inch thick copper grounding
bar affixed to the tower steel about 10-feet above grade (Figure 7).
From there, two heavy-gage copper down-conductors lead to a ring
ground buried around the tower’s base. The ring is bonded to driven,
10-feet x ¾-inch copper-clad electrodes. Also connected to the ring is
a third copper cable. That cable grounds the tower’s steel structure and
is exothermically welded to the tower’s base to ensure durability and
lasting reliability (Figure 8). The coax braid is further grounded at the
exterior and interior firewalls (Figure 5).
FIGURE 8.
The photo on the right shows the reliable, exothermically welded grounding connection to the center cable, which connects the tower’s steel structure to a buried
bare-copper ring ground surrounding the tower and to the interior grounding bar shown in Figure 9.
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• The ring-round and its driven electrodes, plus down-conductors from
the tower and grounding conductors from elsewhere in the facility are
collected at an interior copper grounding bar located on the inside of an
exterior wall just below the space for cable penetrations (Figure 9).
• Finally, all sensitive electronic equipment is properly bonded in its
racks, with cables firmly attached to individual pieces of equipment at
locations that can easily be inspected (Figure 10). The racks themselves
are also grounded.
It should be pointed out that neither the COMTEC facility nor
any of the county’s properly grounded auxiliary transmission
stations have ever experienced a lightning-induced service
disruption. For that, Macomb County residents can thank
smart decisions by COMTEC management, proper design
and installation, regular maintenance, and of course, robust,
all-copper grounding and lightning protection systems.
The Principals
FIGURE 9.
The facility’s interior grounding bar is located on the inside of an exterior wall,
immediately below penetrations for cables from the tower. Various green wires
connect to those cables and to other grounding bars at the facility.
Victoria Wolber is Director of Emergency
Management and Communications for
Macomb County, Michigan. Wolber is a
firm advocate of 100 percent uptime for
the safety center and insisted that the
work of re-structuring the center’s
electrical grounding and lightning protection systems be
undertaken by professionals knowledgeable in the technology. She
can be reached at vicki.wolber@macombgov.org.
Greg Fair is a 20-year veteran project
manager and field superintendent with
Guardian Equipment, a Michigan firm
that specializes in lightning protection.
Guardian designed and installed the
COMTEC center’s grounding and lightning
protection systems working to the three major lightning
protection codes. Fair can be reached at
greg.fair@guardianequipment.com, 248-449-5200.
FIGURE 10.
Properly bonded communications equipment features individual ground leads
to each cabinet. The rack itself is also bonded (not shown). Grounding, bonding
and power feeds for sensitive equipment should be isolated from standard
equipment or lightning circuits.
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